Resist compositions have encountered a new limitation in the field of very small electronic parts. The requirement for producing etched structures of a microscopic dimension on a large scale leads to a demand for those resists which have a higher sensitivity to actinic radiation, which provide a higher contrast, which possess a better spectral sensitivity and, therefore, provide an improved resolving power and a broader processing allowance, and which servo to reduce the unit cost of final electronic devices.
One useful positive type light-sensitive composition contains a polymer having repeating units with photosensitive pendant quinonediazido groups and a monomer which may insolubilize the polymer, where the quinonediazido groups have not undergone decomposition by exposure to actinic radiation. One function of such a monomer is to impart some thermal resistance to the composition by its thermal conversion to a ketene and subsequent cross linking. For example, U.S. Pat. No. 4,365,019 describes 1,3,5-trihydroxybenzene esterified with 1,2-naphthoquinonediazidosulfonic acid as the monomer. A particularly useful polymer is the so-called novolak resin. The image/non-image difference in a diazoketone/novolak photoresist system is determined by the principle of solution inhibition. This diazoketone/novolak system positive type photoresist usually functions very well, but is still insufficient because 1,2-naphthoquinonediazide light-sensitive substances have conventionally been known to be difficult to shift their sensitive wavelength and to spectrally sensitize, and they therefore have been limited as to their application as both resist materials and printing materials such as printing plates.